Field of the Invention
The invention relates to an exhaust gas system for an internal combustion engine, especially an engine for a vehicle and preferably an Otto engine of a vehicle, having a catalytically active device disposed in the exhaust gas system, the device having at least one electrically heatable honeycomb body disposed in a housing for conducting exhaust gas through the body, and the body being connected through electrical lines to connections on the housing.
An electrically heatable honeycomb body, in particular a catalyst carrier body, of the kind that can be used particularly to reduce the pollutant emissions in the coldstarting phase of an Otto engine in motor vehicles, is known from Published International Patent Application WO 92/02714, corresponding to U.S. Pat. No. 5,411,711.
Such a honeycomb body is disposed in a housing that is made of an electrically conductive material and is equipped with electrical connections for the electrically heatable honeycomb body.
The electrical connections are constructed in such a way that an electrical contact between a connection and the housing of the catalytically active device is to be avoided. However, that goal cannot always be reliably met. In rough operation of a motor vehicle, an electrical contact can occur between the electrical line and the housing, for instance from damage to the cable insulation. If an electrical contact occurs between the line carrying a higher electrical potential and the housing, a voltage sparkover can occur, which can cause damage to the connection. The voltage sparkover arises because the housing is electrically connected to the exhaust system, and the exhaust system is connected to ground potential through the engine. The damage to the connections can mean that the honeycomb body can no longer be heated, or can only be heated very unsatisfactorily.
Previously known honeycomb bodies are run on an operating voltage of approximately 12 V. However, demands are being made to run the honeycomb bodies on higher operating voltages. At higher operating voltages, the danger of a voltage sparkover is even greater. That is also true for all of the support and insulating structures which are electrically insulated from the housing and are disposed at the inside of that kind of electrically heatable honeycomb body.